1. Field of the Invention
The present invention relates to a lithium secondary battery, and more particularly, to a lithium secondary battery, which can improve the impregnation of an electrolyte solution either by modifying the material of a protection layer, such as a laminating tape and others, to be formed to protect the elimination of active materials, into a material with an affinity for the electrolyte solution, or by coating the material of an existing protection layer with an ingredient with an affinity for the electrolyte solution.
2. Description of the Related Art
Generally, in accordance with the weight-reduction and high performance of wireless portable devices, such as a camcorder, a cellular phone, a notebook computer and others, there are many studies on the secondary battery used as the power supply therefor. Such secondary battery includes nickel-cadmium battery, nickel-hydrogen battery, nickel-zinc battery, lithium secondary battery and others. Among them, the lithium secondary battery can be recharged and is capable of realizing a size-reduction which providing an increase in capacity. Since the lithium secondary battery has a high operating voltage and a high energy density per unit weight, it is advantageous to be used broadly in high-tech electronics.
In detail, lithium is frequently used as a material for the secondary battery, and has a low atomic weight. Therefore, lithium is a suitable material for the fabrication of a battery with a high energy capacity per unit weight. Meanwhile, lithium reacts violently with water; therefore a non-aqueous electrolyte is used in a lithium-based secondary battery. In this case, since the lithium-based secondary battery is not affected by a decomposition voltage of an electrolysis involving water, it is advantageous to generate an electromotive force (EMF) of approximately 3V to 4V.
The non-aqueous electrolyte used in the lithium secondary battery includes a liquid electrolyte in which a lithium salt is dissociated in an organic solvent, and a solid electrolyte. The organic solvent may include ethylene carbonate, propylene carbonate or carbonate containing other alkyl group or analogous organic compounds.
Such lithium secondary battery mainly uses a lithium-based oxide as a cathode active material and a carbon material as an anode active material. Generally, the lithium secondary battery is classified, based on the kind of electrolytes used therein, into a lithium ion secondary battery using a liquid electrolyte, and a lithium polymer secondary battery using a polymer electrolyte. Further, the lithium secondary battery has been fabricated into various shapes such as a cylindrical shape, a polygon shape and a pouch shape.
Generally, the lithium secondary battery is constructed with an electrode assembly in which a cathode plate coated with a cathode active material, an anode plate coated with an anode active material, and a separator interposed between the cathode and anode plates to prevent the electrical short-circuiting and to enable only the movement of a lithium ion (Li-ion), are wound together, a case for accommodating the electrode assembly, and an electrolyte solution injected into the inside of the case and enabling the movement of a Li-ion, and others.
Such lithium secondary battery is fabricated as follows.
Firstly, the electrode assembly is prepared by laminating the cathode plate coated with the cathode active material and attached with a cathode tab, the anode plate coated with the anode active material and attached with an anode tab, and the separator, and subsequently winding them together. Then, the electrode assembly is accommodated in the case to prevent the separation thereof. Finally, a cylinder-shaped lithium secondary battery is constructed by injecting an electrolyte solution into the case and then sealing the case, while a polygon-shaped lithium secondary battery is constructed by sealing the case with a cap assembly and then injecting the electrolyte solution into the case.
The cathode and anode plates include an active material portion in which an electrode collector is coated with electrode active materials and an electrode uncoated portion composed only of the electrode collector. The adjoining portion between the active material portion and the electrode uncoated portion features a low adhesive force between the active materials and the electrode collector and there is a possibility that the active materials are eliminated, peeled-off or removed from the electrode plate. The elimination of the active materials causes damage on the separator, so that internal short-circuiting may occur. Accordingly, in order to prevent the elimination of the active materials, a laminating tape is attached to the adjoining portion between the active material portion and electrode uncoated portion.
The laminating tape, however, is made from a material that does not have an affinity for the electrolyte solution, and thus the laminating tape can not be sufficiently wetted by the electrolyte solution and enough impregnation of the electrolyte solution is interrupted. Further, in accordance with high capacity battery pack, the interior of the electrode assembly has high density, and it is thus more difficult to become impregnated by the electrolyte solution. Accordingly, there is a need either to modify the material of the laminating tape attached to the interior of the electrode assembly into a material with an affinity for the electrolyte solution, or to coat the interior of the electrode assembly with a material with an affinity for the electrolyte solution, in order to improve the impregnation of the electrolyte solution.